Authors' Names

Presentation Type

Poster Presentation

Area of Focus

Physical and Earth Sciences

Abstract

During the Late Triassic, roughly 200 million years ago, coral reefs flourished and coral diversity was at a maximum. At the end-Triassic, the supercontinent Pangea began splitting at a massive volcanic rift that released prodigious amounts of volcanic greenhouse gases. Ocean pH increased leading to ocean acidification and sea level dropped. Corals reefs responded by collapsing at the end of the Triassic. The transition to the Triassic and Jurassic eras is marked by a major mass extinction at which time more than half of life on Earth and almost 90 percent of marine life died. While the Jurassic recovery was underway during the first few million years following the extinction, corals and reefs did not fully recover until almost 25 million years later. Early Jurassic coral fossils are thus extremely rare. Only a couple Early Jurassic sites have been reported in North America. Precious little is known about coral recovery in western North America where reefs and diverse corals of the Late Triassic inhabited volcanic settings. Scleractinian (stony) corals from the Early Jurassic are not well-represented or studied in North America and until now had not been reported in the United States or Mexico. Here we illustrate previously undescribed Early Jurassic corals from New York Canyon in Nevada, USA, and Sierra de Santa Rosa in Sonora, Mexico. These corals represent the earliest Jurassic appearance in North America and co-occur with other Early Jurassic fossils including bivalves, gastropods and ammonites. In Nevada, the solitary corals occur as both in-situ and reworked specimens belonging exclusively to the family Stylophyllidae. This family is known in North America during the Late Triassic but the Early Jurassic coral represent new species. The composition of these post-extinction corals at New York Canyon reveals an unexpectedly strong connection with Jurassic corals globally. Within the Santa Rosa Formation of the El Antimonio Terrane in Sonora, Mexico, are two previously unstudied fossil reefs containing Early Jurassic colonial corals. Ammonites collected near the locality in the Sierra de Santa Rosa indicate Early Jurassic age. The carbonate reefs are separated by sandstone and mudstone. The interbedded sandstones contain detrital zircon crystals, a mineral that can be radiometrically dated by measuring the decay of uranium to lead. Zircon dating is underway to determine the age of the reefs. Data is used to test paleogeographic and tectonic models for northwestern Sonora and adjacent USA. The Sonoran reefs are perhaps the only Early Jurassic reef examples in the USA and Mexico. These uncommon solitary corals of Nevada and colonial corals of Sonora provide relevant data with which to assess paleoecology, paleobiogeography and biotic recovery during the critical interval following the end-Triassic mass extinction.

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Apr 18th, 2:30 PMApr 18th, 3:50 PM

Newly discovered Jurassic-age fossil coral and implications for North American coral recovery after the end-Triassic mass extinction

UC South Ballroom

During the Late Triassic, roughly 200 million years ago, coral reefs flourished and coral diversity was at a maximum. At the end-Triassic, the supercontinent Pangea began splitting at a massive volcanic rift that released prodigious amounts of volcanic greenhouse gases. Ocean pH increased leading to ocean acidification and sea level dropped. Corals reefs responded by collapsing at the end of the Triassic. The transition to the Triassic and Jurassic eras is marked by a major mass extinction at which time more than half of life on Earth and almost 90 percent of marine life died. While the Jurassic recovery was underway during the first few million years following the extinction, corals and reefs did not fully recover until almost 25 million years later. Early Jurassic coral fossils are thus extremely rare. Only a couple Early Jurassic sites have been reported in North America. Precious little is known about coral recovery in western North America where reefs and diverse corals of the Late Triassic inhabited volcanic settings. Scleractinian (stony) corals from the Early Jurassic are not well-represented or studied in North America and until now had not been reported in the United States or Mexico. Here we illustrate previously undescribed Early Jurassic corals from New York Canyon in Nevada, USA, and Sierra de Santa Rosa in Sonora, Mexico. These corals represent the earliest Jurassic appearance in North America and co-occur with other Early Jurassic fossils including bivalves, gastropods and ammonites. In Nevada, the solitary corals occur as both in-situ and reworked specimens belonging exclusively to the family Stylophyllidae. This family is known in North America during the Late Triassic but the Early Jurassic coral represent new species. The composition of these post-extinction corals at New York Canyon reveals an unexpectedly strong connection with Jurassic corals globally. Within the Santa Rosa Formation of the El Antimonio Terrane in Sonora, Mexico, are two previously unstudied fossil reefs containing Early Jurassic colonial corals. Ammonites collected near the locality in the Sierra de Santa Rosa indicate Early Jurassic age. The carbonate reefs are separated by sandstone and mudstone. The interbedded sandstones contain detrital zircon crystals, a mineral that can be radiometrically dated by measuring the decay of uranium to lead. Zircon dating is underway to determine the age of the reefs. Data is used to test paleogeographic and tectonic models for northwestern Sonora and adjacent USA. The Sonoran reefs are perhaps the only Early Jurassic reef examples in the USA and Mexico. These uncommon solitary corals of Nevada and colonial corals of Sonora provide relevant data with which to assess paleoecology, paleobiogeography and biotic recovery during the critical interval following the end-Triassic mass extinction.